Decoking systems have a container, which slowly fills with coke during the operation of the refinery. This coke must be flushed out from time to time. For this purpose, a decoking tool is introduced into the interior of the container from its top end. The decoking tool is carried by a hollow drill stem, which is connected to a drive which, in the operating state, causes the drill stem to rotate together with the tool. The drill stem is arranged on a slide, which is guided and can be lifted and lowered between sections of a tower above the container. It has a pressurized-water fitting at its top end. The length of the drill stem corresponds at least to the height of the container to be emptied. It is essentially stored, guided and driven outside of the container and is capable of guiding the decoking tool to the bottom of the container.
Decoking, i.e. emptying the coke containers, is carried out using water supplied at a high pressure of more than 100 bar by the drill stem and that shoots out through nozzles arranged on the tool and selectively removes the coke deposited in the interior of the container. During decoking, the tool traverses the entire height of the interior along the longitudinal axis of the container. Once the coke has been flushed out, the decoking tool is retracted into a rest position at the top end of the container. With regard to the good functioning of this tool together with its guiding, it must be taken into consideration that the coke container expands or contracts depending on the temperature during operation of the refinery. Due to the size of the container, deformations result changing the position of the guiding of the drill stem of the decoking tool. The drill stem of the decoking tool should be suspended precisely below the drive of the tool. Due to the thermally induced shape variations of the container, however, there is a displacement of a guide plate mounted at the top of the decoking container or above the same, usually flanged there, if necessary, with the interposition of a valve or a slide and an adapter, and on which the drill stem is guided, which connects the decoking tool and the drive. The forces applied to the drill stem by the displacement of the guide plate, are undesirable. They lead to the drill stem being prematurely worn.
The exposure of the drill stem to such undesirable forces due to the thermally induced deformation of the container occurs both in the case that centering of the drill stem is carried out directly or indirectly on the container, and in the case that the drill stem is guided in the tower above the container and relative displacements arise between the tower and the container. In the latter case the container, if deformed due to thermal stresses, is no longer centered below the tower where the drill stem is guided.
It is known from the state of the art to enlarge the opening in the guide plate through which the drill stem is guided. It is thus avoided that the drill stem is undesirably deflected by radial forces. However, the drill stem is no longer sufficiently guided, it wobbles in the operating state and is damaged thereby. Consequently, this prior art approach is not satisfactory.